In an energy delivery device (e.g., a battery cell), electric current is carried from a battery electrode foil to a centrally located terminal. The electrode foil can be directly connected to the central terminal, or it can be connected to the central terminal through a current collecting tab (e.g., a thin strip of metal). In some conventional energy delivery devices, the orientation of the plane of the foil or tab at the location in which it connects to the central terminal largely coincides with the longitudinal axis of the cell. Employing such a vertical connection requires considerable vertical space in the cell.
Other conventional energy delivery devices use a horizontal tab connection. FIG. 1 illustrates such a device 102. In device 102, tabs 110 are connected to electrode 108 at the lower end, and are connected to a central terminal 114 at the upper end. The central terminal 114 has a protruding post 104 that is connected to a bolt 112. The tabs 110 have holes (not shown) at the upper end and the protruding post 104 protrudes through the holes. During assembly, the upper ends of the tabs 110 are stretched over to the top of the post 104 and then pressed down with the post 104 passing though the holes. This requires the lengths of the tabs 110 to reach from the points of connection with electrode 108 to the top of the post 104, which are longer than the horizontal distances between the points of connection with electrode 108 and the center of the cell 102. Cell 102 also suffers from high electrical impedance because current coming out of the electrode 108 passes through mechanical connections 106. For example, the connection between the post 104 and the bolt 112 is a threaded connection. The tabs 110 are connected to the terminal 114 at the bottom of the post 104 by placing a nut 116 on top of the tabs 110. These mechanical connections 106 tend to have high impedance. Some conventional cells have multiple components through which current must be conducted, which adds impedance.
Therefore, it is desirable to employ a low impedance cap assembly that is space efficient and does not require an extra tab length.